Spearmint

Identification and origin

Mentha spicata belongs to the family Lamiaceae, along with thyme, basil, and rosemary. Its native range is huge: much of Europe, from southern Scandinavia to the shores of the Mediterranean, Turkey, the Caucasus, Iran, and Central Asia, then the Himalayas, Tibet, and southern China, as well as Egypt and the Sinai. In the wild it grows in moist meadows and along the edges of ponds and lakes.

It is an upright herbaceous perennial that usually reaches 12 in – 2 ft tall and as wide, sometimes up to 3.5 ft. Its stems are square, as in all Lamiaceae, and it spreads by underground rhizomes; the stems also root wherever they touch the ground. The bright green leaves are oval and pointed, 2–4 in long, with toothed edges. It can be told apart from other mints by its nearly hairless leaves, which have little or no leaf stalk; the surface looks wrinkled because of the sunken veins.

In summer, small lilac, pink, or white flowers open in slender, interrupted spikes 1–6 in long at the stem tips. They attract bees and butterflies, and each flower is followed by four tiny nutlets. The genus name comes from Minthe, a nymph turned into a plant in Greek mythology; the epithet spicata means “spiked.” The cultivar ‘Kentucky Colonel’ is noted for the quality of its foliage.

Light

Full sun or part shade: aim for at least four to six hours of direct sun a day. In a container, moving the pot into part shade during hot spells slows drying and cuts down on watering.

Watering

Spearmint likes moist soil and does poorly in dry conditions. In the ground, water new plantings until they are established, then during the growing season whenever the soil dries out, especially in hot, dry weather. In a container the root ball dries out much faster: check it often while the plant is growing and water as soon as the surface of the mix is dry, to keep it evenly moist.

Moist does not mean soggy. Too much water encourages root rot and foliage diseases. Water at the base of the plant, ideally before midday, so the leaves don’t stay wet overnight, which favors rust.

Potting mix

It adapts to nearly any soil, clay, loam, sand, or chalk, but does best in soil rich in organic matter, moist and well drained, with a slightly acidic to neutral pH of about 6 to 6.5. In a container, use a peat-free multipurpose or soil-based potting mix.

Growing it in a container is strongly recommended, because it spreads quickly and crowds out its neighbors. A pot 12–16 in across works well. In the garden, sink a large bottomless pot: leave the rim a few inches above ground and bury it 10–15 in deep, so the rhizomes are forced up over the rim, where you can trim them before they root elsewhere.

Soil amended with compost is usually enough. If needed, a single application of slow-release complete fertilizer in early spring covers the season: too much fertilizer and too much water encourage rust and reduce the essential oil content.

Temperature

This is a very hardy plant that survives about -20 °F in the ground; it is grown in USDA zones 4a to 9b. The top growth dies back in winter and new shoots emerge from the rhizomes in spring. Seedlings, however, are frost-sensitive: move them outdoors only after the danger of frost has passed.

Repotting

Spearmint quickly wears itself out in a container that is too small. Every two or three years, take the clump out of its pot, discard the old center, and replant a vigorous section in the same pot with fresh mix, or move it to a bigger pot. In the garden, divide clumps every three or four years to keep the plants vigorous.

Pruning

Harvest often: the more you cut, the more young shoots the plant produces, and these have the best flavor. Start harvesting once the plant is 3–4 in tall, cutting stems close to the ground. Flower spikes lower the oil content and flavor of the leaves; pinch them off as they appear or, after flowering, cut the whole clump back to 2 in above the ground: tender new shoots follow within a few weeks. It is hard to overprune spearmint; you can cut it back this way two or three times a season.

At the end of the season, cut faded stems to the ground to discourage pests and diseases. To dry spearmint, cut stems just as flowering begins and hang them upside down in a warm, shady spot.

Propagation

Division is the simplest method: in spring before growth starts, or in early fall, cut the root ball into several pieces with a knife or spade, discard any dead parts, and replant each division.

Cuttings are just as easy. In spring, take soft new shoots; they root in potting mix or even in a glass of water and can then be potted up. Pieces of rhizome also regrow readily.

Seed can be sown indoors in spring: scatter it on the surface without covering, under a clear lid, at about 68 °F, then move the seedlings into 3–3 in pots. But mints cross easily with one another and seedlings often differ from the intended variety: for a specific flavor, start from a cutting or a division.

Common problems

• Powdery orange, yellow, then black spots, mostly on leaf undersides: mint rust. Remove affected stems, avoid wetting the foliage, and don’t overfeed.
• Spots on the leaves: leaf spot diseases.
• White powdery coating on leaves: powdery mildew.
• Curled, yellowed leaves and stunted shoots: aphids; knock them off with a jet of water or use insecticidal soap.
• Chewed leaves: mint moth caterpillars or blue mint beetle.
• Other possible insects: leafhoppers.
• Young stems cut off at ground level: cutworms.
• Yellowing that starts at the leaf edges, then leaves curl up and die: pull out affected plants and replant in a different spot.

The same symptom can have several causes: always check watering, sunlight, fertilizing, and the leaf undersides before drawing conclusions.

Toxicity

Mints are toxic to dogs, cats, and horses: their essential oils cause vomiting and diarrhea when an animal eats a large amount. For people, toxicity is low and only a concern with very large ingestions; the plant does not cause contact dermatitis. Buy correctly labeled plants: pennyroyal, another mint species, is harmful if eaten.